IMO, scienceforums.net is the only one that comes close. If you go there look for swansont, Severian, Martin, and dave for physics/math stuff. You can also find some PF regulars there, such as Janus, Matt Grime, and myself.

I could post links to 10 other forums that claim to be dedicated to science, but I wouldn't be doing you any favors by doing so. Most are unmoderated or have no committment to academic or scientific integrity.

what makes this site so special? I personally love this place,that's why i've given money to it. But what is the dynamic that makes this site "work" while others do not? how long has this site been around?

It's hard to isolate one "ingredient" of the physicsforums.com recipe as that which makes the site the best on the web. We have an unbelievably qualified and dedicated staff, we have thousands and thousands of intelligent, well-spoken members. We have math typesetting. We have loads of google traffic. We help tons of kids with their homework. We have professional physicists, astronomers, biologists, chemists, and more (many of them, in fact!). We are a relatively strongly-censored forum, in that we have a no-nonsense policy. We quickly eliminate spam, off-topic nonsense, crackpot theories, and the like. We try to keep the overall quality of posts very high here; in the process we do, in fact, turn away a lot of people. Perhaps the "closed" nature of the forum is what makes it work so smoothly.

I guess we've got a good owner.Greg's got other sites,too.The forum's advertised there,too.The homework idea was & still is a real hit.I mean,just think how many lazy people are in this world.The success was guaranteed.

It's all about marketing and knowing that an info,a reccomandation or a piece of advise is worth a lot.